Validating Self-Report Measures of Pain and Function in Patients Undergoing Hip or Knee Arthroplasty

PURPOSE: To investigate the factorial and construct validity of a four-item pain intensity scale, the P4, in patients awaiting primary total hip or knee arthroplasty secondary to osteoarthritis. METHOD: A construct validation design was applied to a sample of convenience of 117 patients (mean age 65.6 [SD = 11.2] years) at their preoperative visit. All patients completed the P4 and the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). Exploratory and confirmatory factor analyses were used to examine the factorial structure of the P4 and WOMAC. To evaluate construct validity, we examined the correlation between the P4 and WOMAC pain sub-scales and the ability of the P4 to differentiate between patients awaiting hip and knee replacement. RESULTS: Two distinct factors consistent with the themes of pain and function were identified with P4 and WOMAC physical function items, but not with the WOMAC pain and physical function items. The P4 correlates more with the WOMAC pain scores (r = 0.67) than with the WOMAC physical function scores (r = 0.60). CONCLUSION: The P4's validity was supported in this patient group. The use of the P4 with the WOMAC physical function sub-scale provides a more distinct assessment of pain and function than the WOMAC pain and physical function scales.